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IPv6 Essentials
book

IPv6 Essentials

by Silvia Hagen
July 2002
Beginner content levelBeginner
360 pages
11h 19m
English
O'Reilly Media, Inc.
Content preview from IPv6 Essentials

Prefix Notation

The notation for prefixes has also been specified in RFC 2373. A format prefix is the high-order bits of an IP address used to identify the subnet or a specific type of address (refer to Table 3-2). In newer drafts, it is called the global routing prefix. The prefix notation is very similar to the way IPv4 addresses are written in Classless Interdomain Routing (CIDR) notation, and it is also commonly used for subnetted IPv4 addresses. The notation appends the prefix length, written as a number of bits with a slash, which leads to the following format:

IPv6 address/prefix length

The prefix length specifies how many left-most bits of the address specify the prefix. This is another way of noting a subnet mask. Remember, a subnet mask specifies the bits of the IPv4 address that belong to the network ID. The prefix is used to identify the subnet that an interface belongs to and is used by routers for forwarding. The following example explains how the prefix is interpreted. Consider the IPv6 prefix notation 2E78:DA53:12::/40. To understand this address, let’s convert the hex into binary as shown in Table 3-1.

Table 3-1.  Understanding prefix notation

Hex notation

Binary notation

Number of bits

2E 78

DA 53

12

00101110 01111000

11011010 01010011

00010010

16 bits

16 bits

8 bits, total 40 bits

The compressed notation (replacing a sequence of zeros with a double colon) is also applicable to the prefix representation. It should be used carefully, though, ...

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Publisher Resources

ISBN: 0596001258Catalog PageErrata